A major objective of our research is to obtain a better understanding of the biochemical, physiological and anatomical adaptations responsible for the increases in endurance and in maximum work capacity that occur in response to endurance exercise. We have, so far, found that endurance exercise results in an increase in the respiratory capacity of skeletal muscle as a result of an increase in muscle mitochondria. We now aim to determine whether this increase in mitochondria is due to an increase in the rate of synthesis of mitochondrial proteins, a decrease in the rate of mitochondrial degradation or a combination of the two; our approach will be to study the turnover of mitochondrial proteins. Another of our aims is to discover which of the acute chances in cellular homeostasis associated with exercise are responsible for the adaptive increases in mitochondria and myoglobin in skeletal muscle. A second major objective is to obtain information regarding the causes for muscle fatigue, including the roles of glycogen depletion in liver and skeletal muscle, of lactate accumulation in muscle, and of impairment of the contractile process. A third major objective is to obtain information on the effects of regularly performed exercise on certain aspects of the aging process and on longevity. A fourth major objective is to elucidate the mechanisms by which exercise lowers serum triglyceride levels.